Sol-gel chemistry has been used for many years. Most research has been directed towards inorganic gels created by hydrolysis of metal alkoxides. NASA has developed aerogels where the strength and the heat insulation properties of these materials have been optimized. Many other scientists have been reporting on the use of gels and aerogels for control of drug delivery. Here the gel performs the role as a sponge absorbing medically active compounds for later slow release. The process of interest is here diffusion out of the inert gel material. Yet another direction of research has been to encapsulate large molecules like proteins or even live bacteria or cells into the gel network. It has been found that in many cases the enzymes encapsulated in the gel retain their activity. In special cases as observed with Lipases they may even display significantly enhanced activity when located in the gel network. The gel is thus used as a bioreactor where the enzyme is staying fixed while the reactants and the products diffuse in and out of the very open gel network. Also in these last two situations it is important that the gel is strong and that it can retain its properties during the processes.
Aerogel particles have been proposed for use in controlled release of pharmaceuticals, see e.g. U.S. Pat. No. 6,994,842 B2.
Active compounds are a necessity for protection against biological growth in the coatings field. Due to environmental restrictions against traditional biocides and fungicides the need for more environmentally acceptable solutions is growing. Even though attempts to use enzymes and/or other organic molecules can be found in literature the success is restricted. Incorporating this type of molecules in a paint or coating is not an easy task.
In paints containing enzymes such as proteases the water-borne systems may have stability problems since sedimentation during storage result in a pigment and binder precipitate and a water enzyme liquid phase. During storage the enzyme react in an autodegradation whereby the enzyme activity is significantly reduced. For this purpose it would be highly significant if the enzyme could be prevented from degradation during storage.
There is also a need to keep the active compound on the coating surface in an effective dosage to get a proper protection.
Furthermore it must be considered that different types of coatings depending on the application probably will need different solutions to the dosage problem.
Aerogels have been known to be useful as additives in paint formulations since they among other properties may introduce thixotropic properties. This property allows industrial spraying of thicker films of good quality. WO 2002/074868 discloses thixotropic paint formulations comprising silica aerogel.